2,5-Dioxo-3-Pyrroline (1H-Pyrrole-2,5-Dione) Detailed Information, Properties, Uses & Safety

Incorporation of maleimide monomer into bismaleimide (BMI) prepreg formulations for autoclave-cured carbon fibre-reinforced polymer (CFRP) structures is driven by the need to reduce melt viscosity while preserving the aromatic imide network’s thermo-oxidative stability above 230°C. The compound 1H-pyrrole-2,5-dione (CAS 541-59-3) functions as a reactive diluent that participates in the addition-cure mechanism, lowering the minimum viscosity of a standard 4,4′-bismaleimidodiphenylmethane (BMI-MDA) resin from approximately 8–12 Pa·s to 0.5–2 Pa·s at 120°C when dosed at 12–18 wt% of the total resin mass. This viscosity reduction enables void-free impregnation of heavy-tow carbon fabrics (12K–24K filaments) on automated fibre placement (AFP) lines operating at lay-down speeds exceeding 30 m/min. Processing constraints are narrow: the formulated resin must remain at <100°C during prepregging to prevent premature vinyl addition, and post-layup cure cycles typically follow a stepped ramp of 2°C/min to 180°C with a dwell of 4 hours, followed by a free-standing post-cure at 250°C for 6 hours. Violation of the ramp rate or inadequate vacuum hold before autoclave pressurisation leads to microvoid formation at ply interfaces, detectable via C-scan attenuation exceeding 6 dB. Compliance is demonstrated through ASTM D7028-07e1 glass transition temperature measurement by DMA, where tan δ peak must exceed 280°C; ASTM D790-17 flexural properties retained to 85% at 232°C after 500 hours of thermal ageing per ASTM D3045-18; and flammability resistance meeting FAR 25.853(a) Appendix F Part I vertical burn with self-extinguishing times under 15 seconds and burn length below 152 mm. Incompatibility exists with amine-based curing agents such as diaminodiphenyl sulfone: even trace contamination (<0.1 wt%) triggers Michael addition of the maleimide double bond at temperatures as low as 60°C, producing a gel particle population that clogs resin infusion gates. Terminal components include fan containment cases for next-generation turbofan engines, missile radomes requiring dielectric constant below 3.2 at 10 GHz, and satellite edge members where coefficient of thermal expansion must not exceed 15 ppm/°C in-plane.

**Rheological and thermomechanical response of BMI-MDA/maleimide blends (isothermal hold at 120°C)**
Maleimide addition (wt%)	Minimum complex viscosity η* (Pa·s)	Tg by DMA (tan δ, °C)	Gel time at 150°C (min)
0	9.8	295	42
8	3.4	291	38
15	1.1	286	35
20	0.6	272	33

Pre-drying of maleimide monomer is mandatory when ambient relative humidity exceeds 60%, as adsorbed moisture accelerates ring-opening hydrolysis to maleamic acid, which decarboxylates at cure temperature to generate CO₂-induced porosity. Vacuum oven treatment at 40°C and <10 mbar for 16 hours reduces free water content to <200 ppm by Karl Fischer titration, a threshold below which internal void fraction measured by image analysis of polished cross-sections stays below 0.5 vol%.

Concurrent with free-radical graft copolymerisation of polypropylene in a co-rotating twin-screw extruder (L/D 40:1, screw diameter 25 mm), maleimide is fed downstream into the melt to introduce polar imide sites onto the polymer backbone, improving interfacial adhesion with glass fibre reinforcement in injection-moulded automotive components. The grafting reaction is initiated with 0.3–0.7 wt% dicumyl peroxide, while maleimide is metered at 1.5–3.0 wt% relative to PP. Barrel temperatures are profiled from 180°C at the feed throat to 220°C at the die, with a residence time of 45–60 seconds. Excess unreacted monomer is devolatilised under vacuum (−0.08 MPa) at the penultimate zone. Grafted maleimide content, determined by nitrogen elemental analysis via ASTM D5291-21, ranges from 0.6 to 1.2 wt% depending on peroxide loading. Compliance matrix for automotive under-the-hood applications references ASTM D638-14 tensile properties, ASTM D256-23 notched Izod impact at −30°C, and ASTM D648-18 heat deflection temperature under 1.82 MPa load. Long-term thermal oxidative stability is assessed per ISO 4577:2019 at 150°C for 1 000 hours, with retained tensile strength required to exceed 80%. The maleimide-grafted PP is compounded with 30 wt% short glass fibre in a second extrusion pass. Terminal parts include integrated air intake manifolds with burst pressure ratings above 8 bar at 120°C and battery housing components for electric vehicles requiring comparative tracking index (CTI, IEC 60112:2020) above 600 V. When processing maleimide-grafted materials, screw recovery time must be adjusted for reduced melt flow index; a drop from 12 g/10 min (base PP) to 3–5 g/10 min (grafted compound) necessitates a clamp force of at least 4 kN/cm² projected area to avoid flash during mould filling.

What Happens When Maleimide Replaces a Fraction of the Epoxy Curing Agent in Mold Compound Formulations?

Replacing 15–25 mol% of a cresol novolac epoxy hardener with a monofunctional maleimide such as N-(p-carboxyphenyl)maleimide shifts the thermal decomposition onset of a silica-filled semiconductor encapsulant from 380°C to approximately 405°C as measured by thermogravimetric analysis (ASTM E1131-20) at 10°C/min in nitrogen. The maleimide is pre-dissolved in the epoxy resin at 80°C before filler addition. The final compound contains 82–85 wt% spherical fused silica (D50 12 μm), maleimide at 1.8–2.4 phr relative to resin solids, triphenylphosphine catalyst at 0.5 phr, and carnauba wax mould release at 0.3 phr. Mixing is conducted on a two-roll mill with cooling water inlet at 12°C to prevent batch temperature exceeding 50°C and unintended imide homopolymerisation. Transfer moulding at 175°C and 70 kg/cm² transfer pressure yields packages with IPC-4101E Class H dielectric properties: dielectric constant 3.8 and dissipation factor 0.012 at 1 MHz. Post-mold cure of 4 hours at 180°C is critical to achieve 85% conversion of maleimide as confirmed by FTIR disappearance of the 830 cm⁻¹ out-of-plane vinyl CH wag. The moulding compound achieves UL 94 V-0 at 0.8 mm thickness with an oxygen index above 36% (ASTM D2863-23). Wire bonding reliability is tested after 192 hours of unbiased HAST (JESD22-A118B, 130°C/85% RH) with gold bond lift-off failures below 50 ppm. This formulation is utilised in quad-flat no-leads (QFN) packages and ball grid array (BGA) substrate coatings where lead-free solder reflow survivability at 260°C peak temperature per J-STD-020E MSL 3 is mandatory. A limitation of maleimide-epoxy systems is the exothermic peak broadening observed by DSC above 25 mol% substitution, which can extend press cycle time from 90 seconds to over 140 seconds when gelation at the runner entrance occurs before complete cavity filling.

Thermal Reversion Resistance in Sulphur-Crosslinked Diene Rubber Compounds

Addition of N-phenylmaleimide at 0.5–2.0 phr to a natural rubber truck tyre tread compound during the second stage of a 270-litre intermeshing internal mixer counteracts anaerobic thermal reversion of polysulphidic crosslinks that propagates above 150°C in service. The Diels–Alder adduct formed in situ between maleimide and conjugated diene sequences traps chain scission products, preserving crosslink density as measured by equilibrium swelling in toluene (ASTM D6814-02(2024)) and reflected in a Moving Die Rheometer cure curve (ASTM D5289-19a) that shows a plateau torque (M_H) decline limited to <5% after 60 minutes at 180°C, compared to 25–30% loss in unprotected controls. The compound formulation includes NR (100 phr), N330 carbon black (50 phr), zinc oxide (5 phr), stearic acid (2 phr), sulphur (2.5 phr), CBS accelerator (0.8 phr), and maleimide added in a dump-extrusion masterbatch step where stock temperature must not exceed 110°C to prevent scorch as measured by a Mooney viscometer t₅ at 135°C (ASTM D1646-19) dropping below 8 minutes. Sheet finalising is performed on a two-roll mill with friction ratio 1:1.2 at 40°C. Vulcanisation in a multi-daylight press at 150°C for t₉₀ + 5 min produces tensile sheets with sustained elongation at break above 450% after hot air ageing 72 hours at 100°C (ISO 188:2023). The compliance framework references ISO 37:2017 for tensile stress-strain properties and ASTM D5964-16 for rubber property—abrasion resistance using a DIN abrader with 10 N load. End products include off-highway tyre shoulder regions and conveyor belt covers for hot particulate matter transport where intermittent skin temperatures reach 160°C. A compounding risk arises if maleimide exceeds 3.0 phr: excess unreacted monomer blooms to the surface within 48 hours at 23°C, creating a dusty deposit that reduces inter-ply green tack to <2 N/mm as determined by peel test on an unvulcanised laminate.

Assembly of High-Temperature Structural Adhesive Films with Maleimide-Toughened BMI Matrices

A structural film adhesive formed by solvent-casting a mixture of BMI oligomer (60–70 wt%), maleimide (12–18 wt%) as viscosity modifier, carboxyl-terminated butadiene-acrylonitrile rubber (CTBN, 10–15 wt%), and an inert polyimide thermoplastic powder (5–8 wt%) is calendered to 200 μm dry thickness on a release paper support for secondary bonding of aluminium alloy airframe components. The maleimide monomer, with a melting point of 94°C, assists in film formation by coalescing the BMI particles during the 50°C B-staging step without initiating cure, verified by DSC isothermal hold showing exotherm onset delayed beyond 120 minutes. The adhesive is co-cured with the metal adherend at 177°C for 2 hours under 0.3 MPa pressure. Single-lap shear strength on chromic acid anodised 2024-T3 aluminium (ASTM D1002-10(2019)) reaches 28 MPa at −55°C, 24 MPa at room temperature, and 14 MPa after 10 minutes soak at 232°C. Floating roller peel resistance (ASTM D3167-10(2021)) yields 6.2 N/mm. These values satisfy the requirements of MMM-A-132B Type I Class 3 for metal-to-metal structural adhesives in bonded repair of helicopter tail rotor blades and fixed-wing leading edge panels. Durability is validated by 30-day salt spray exposure (ASTM B117-19) with lap shear retention above 90%. Pre-bond humidity exposure at 85% RH for 24 hours prior to layup causes a drop in lap shear to 18 MPa unless the film is re-dried at 80°C for 30 minutes, emphasising the hygroscopic tendency of the maleimide carbonyl group.

Maleimide derivatives exhibiting an acrylate-free photopolymerisable double bond are formulated into UV-curable hard coatings for polyethylene terephthalate (PET) display films, where crosslink density and pencil hardness must meet ASTM D3363-20 specifications of at least 4H at 3 μm cured thickness. N-(2-hydroxyethyl)maleimide is dissolved at 8–12 wt% in a mixture of aliphatic urethane acrylate oligomer and trimethylolpropane triacrylate, with a Type I photoinitiator (2 wt% diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide) activated by a 395 nm UV-LED array delivering 600 mJ/cm² in-air traversing at 12 m/min. The maleimide co-monomer raises the glass transition temperature of the coating from 62°C to 91°C (dynamic microhardness indentation, ISO 14577-4:2016) and reduces Taber haze after 100 cycles of CS-10F abrasion under 250 g load from 12% to 4% (ASTM D4060-14). The coating must meet IEC 62321-8:2017 restrictions on phthalates and the RoHS recast directive (2011/65/EU) for homogeneous materials. Adhesion to untreated PET, tested by cross-hatch tape pull (ISO 2409:2020), remains at classification 0 provided the film surface is corona-treated to a dyne level above 50 mN/m immediately before slot-die coating. End products are anti-glare touch panel overlays and flexible display cover lenses. Formation of a tack-free surface requires inert nitrogen blanketing at <200 ppm residual oxygen during UV exposure; ambient curing in air results in a residual unsaturation exotherm and surface energy above 44 mN/m, which elevates fingerprint affinity.

**Grafting efficiency and mechanical balance of maleimide-modified polypropylene (twin-screw, L/D 40:1, 220°C die)**
Peroxide/wt%	Maleimide/wt%	N content/wt%	Grafting efficiency/%	Notched Izod −30°C J/m	MFI 230°C/2.16 kg g/10 min
0.3	1.5	0.42	62	48	8.2
0.5	2.0	0.78	71	55	5.7
0.7	3.0	1.15	68	63	3.1

Can Maleimide Serve as a Low‑Molecular‑Weight Alternative to Bismaleimide in High‑T_g Thermosets?

Maleimide and BMI resins occupy distinct roles in high‑temperature thermoset design. A direct comparison of 2,5‑Dioxo‑3‑pyrroline~1H‑pyrrole‑2,5‑dione (MAI‑99) with a standard 4,4′‑bismaleimidodiphenylmethane (BMI‑1000, melting point 155–160°C) illustrates the fundamental divergence in crosslinking architecture (Table 1). Radical homopolymerization of maleimide produces linear poly(maleimide) with a mid‑point glass transition temperature of 185°C (ASTM D3418‑15, heating rate 10 K·min⁻¹) and a storage modulus of 3.2 GPa at 30°C (ASTM D4065‑20), whereas BMI‑1000 after thermal cure (2 h at 200°C + 4 h at 250°C) yields a crosslinked network with T_g 325°C and onset of degradation (5% mass loss) at 420°C in nitrogen (ASTM E1131‑08). Maleimide, therefore, cannot replace BMI in applications demanding thermomechanical stability beyond 200°C without a co‑monomer that generates a network. Instead, it is employed as a reactive diluent to lower melt viscosity: addition of 10 phr maleimide to a BMI resin reduces the minimum complex viscosity at 140°C from 12.5 Pa·s to 0.8 Pa·s (oscillatory shear, 1 rad·s⁻¹, parallel‑plate geometry), facilitating resin transfer molding (RTM) operations. When used with aromatic diamines such as 4,4′‑diaminodiphenylmethane, maleimide participates in Michael addition chain extension, producing linear poly(aspartimide) with T_g of 210°C; however, the absence of crosslinks leads to a lap‑shear strength (ASTM D1002‑10) of 12 MPa on aluminum substrates, well below the 24 MPa achieved with BMI/diamine networks.

Property	2,5‑Dioxo‑3‑pyrroline~1H‑pyrrole‑2,5‑dione (MAI‑99)	4,4′‑Bismaleimidodiphenylmethane (BMI‑1000)
Molecular weight (g·mol⁻¹)	96.04	358.35
Functionality	1	2
Melting point (°C)	92–94	155–160
Homopolymer T_g (°C, ASTM D3418)	185	325
Minimum complex viscosity at 140°C (Pa·s)	0.02	12.5
Water absorption at 25°C, 50% RH (wt%)	4.2 (hydrolysis risk)	1.1

Property

2,5‑Dioxo‑3‑pyrroline~1H‑pyrrole‑2,5‑dione (MAI‑99)

4,4′‑Bismaleimidodiphenylmethane (BMI‑1000)

Molecular weight (g·mol⁻¹)

96.04

358.35

Functionality

Melting point (°C)

92–94

155–160

Homopolymer T_g (°C, ASTM D3418)

185

325

Minimum complex viscosity at 140°C (Pa·s)

0.02

12.5

Water absorption at 25°C, 50% RH (wt%)

4.2 (hydrolysis risk)

1.1

Reaction Enthalpy and Dynamic Gel Point Control in Furan‑Maleimide Reversible Networks

Maleimide acts as a dienophile in thermally reversible Diels‑Alder (DA) adduct formation with furan derivatives, a mechanism exploited in re‑processable covalent adaptable networks. When maleimide is mixed with furfuryl alcohol (FA) at a stoichiometric ratio of 1:1 (maleimide:FA), differential scanning calorimetry (DSC Q2000, ISO 11357‑1:2016) reveals an exothermic event with onset at 42°C and a total enthalpy of −110 J·g⁻¹ (heating rate 10 K·min⁻¹). The reverse reaction (retro‑DA) initiates at 85°C, with an endotherm of +98 J·g⁻¹, establishing a processing window of 43°C. Dynamic oscillatory rheometry (TA ARES‑G2, 25 mm parallel plates, gap 0.5 mm, frequency 1 Hz) monitors gelation at 60°C: the crossover of storage and loss moduli occurs at 18 min ± 2 min for the stoichiometric system and shifts to 52 min when 5% excess maleimide is used. A critical processing limitation is that exotherm containment demands active cooling; a 2 g batch experiencing adiabatic temperature rise can exceed 85°C within 90 s, triggering premature network depolymerisation that reduces the final crosslink density measured by equilibrium swelling in DMF by 40% (ASTM D2765‑16). Multi‑day creep recovery tests (ASTM D2990‑17) at 70°C demonstrate 95% strain recovery after 24 h for networks cured within the 60–80°C range, whereas samples exposed to 90°C during cure retain only 62% recovery due to irreversible chain scission.

Production of maleic anhydride‑grafted polypropylene (PP‑g‑MAH) on a co‑rotating twin‑screw extruder (screw diameter 26 mm, L/D = 40, barrel zones 10) benefits from downstream addition of maleimide as a radical‑scavenging co‑agent. A barrel temperature profile of 180°C (feed) to 210°C (die) and screw speed of 300 rpm generate a specific mechanical energy input of 0.28 kWh·kg⁻¹. Maleimide powder, pre‑dried at 40°C under vacuum (≤10 mbar) to a moisture content <0.05%, is metered via a side‑stuffer into barrel zone 7 at a dosage of 0.5–1.2 wt% relative to the PP‑g‑MAH melt stream. The imide radical adduct suppresses β‑scission and increases grafting efficiency from a baseline of 0.47% bound maleic anhydride to 0.82% (titrimetric determination, ASTM D6474‑20). Melt flow index (MFR, 230°C, 2.16 kg, ISO 1133‑1:2022) drops from 48 g·10 min⁻¹ to 22 g·10 min⁻¹, consistent with molecular weight retention. However, local overheating above 220°C triggers imide homopolymerisation and cross‑linking, manifesting as a sudden torque increase of 12–18% and surface irregularities on the extrudate. Therefore, melt temperature sensors positioned at the mixing zones must alarm at 215°C. Avoid combining maleimide with amine‑based stabilisers during extrusion; prematurely formed maleamic acid adducts reduce radical scavenging efficiency by 34% (measured as residual graft level).

Thiol‑Maleimide Coupling Kinetics Measured Under Biopharmaceutical Processing Constraints

The Michael‑type addition of a thiol to the maleimide double bond is a workhorse reaction in bioconjugation, but the mono‑functionality of 2,5‑Dioxo‑3‑pyrroline~1H‑pyrrole‑2,5‑dione eliminates the risk of cross‑linked aggregates that arise with bis‑maleimide linkers such as bismaleimidoethane. Pseudo‑first‑order rate constants determined by stopped‑flow fluorescence (phosphate buffer, I = 0.15 M, 25°C) are 5.2 × 10³ M⁻¹s⁻¹ at pH 7.4 and drop to 1.1 × 10³ M⁻¹s⁻¹ at pH 6.5, owing to the thiolate anion concentration dependence. The competing ring‑opening hydrolysis, however, becomes kinetically significant at pH 8.0, where the maleimide half‑life is 8 h. A quality‑control release criterion for bioconjugation‑grade material is a residual maleamic acid content <1.5% by ¹H NMR (DMSO‑d₆, 400 MHz, ASTM E386‑90(2011)). Conjugation protocols targeting 85–92% efficiency at protein concentrations of 5 mg·mL⁻¹ employ a 1.5‑fold molar excess of maleimide over free thiols and a reaction time of 2 h at 22°C. In contrast, commercial maleimide‑terminated PEGs frequently contain 2–5% inactive maleamic acid, which leads to batch‑to‑batch variability in conjugate purity and must be verified by ion‑exchange chromatography (IEC). Molecular sieving challenges arise when maleimide is used directly without a solubilising spacer: the small molecule (96 Da) can penetrate the protein core and label buried cysteines, an effect not observed with PEG‑maleimide 2 kDa conjugates. Published data for this specific configuration on large‑scale GMP manufacturing are limited, but in‑house process development batches indicate a filterability index through 0.2 µm polyethersulfone membranes of V_max = 48 L·m⁻² when using 0.3 M sodium chloride to suppress non‑specific binding.

Quality‑control release data for grade MAI‑99 (lot‑to‑lot consistency over 12 consecutive production batches) are summarised in Table 2. Each parameter is verified in accordance with the stated analytical protocol prior to shipment in 25 kg fibre drums with aluminium‑laminated polyethylene liners, purged with nitrogen to a residual oxygen level <0.5%.

Parameter	Method	Typical value	Acceptance limit
Assay (anhydrous, wt%)	HPLC‑UV 254 nm	99.4%	≥99.0%
Water content	Karl Fischer, ISO 760:1978	112 ppm	≤150 ppm
Melting point	ASTM E324‑16	93.1°C	92.0–94.0°C
APHA colour (10% in acetone)	ASTM D1209‑05(2019)	30	≤50
Maleamic acid	¹H NMR	0.4%	≤1.5%
Residual solvent (acetone)	GC‑HS, USP <467>	28 ppm	≤100 ppm

Parameter

Method

Typical value

Acceptance limit

Assay (anhydrous, wt%)

HPLC‑UV 254 nm

99.4%

≥99.0%

Water content

Karl Fischer, ISO 760:1978

112 ppm

≤150 ppm

Melting point

ASTM E324‑16

93.1°C

92.0–94.0°C

APHA colour (10% in acetone)

ASTM D1209‑05(2019)

≤50

Maleamic acid

¹H NMR

0.4%

≤1.5%

Residual solvent (acetone)

GC‑HS, USP <467>

28 ppm

≤100 ppm

If Maleimide Is Co‑polymerized with Methyl Acrylate via Conventional Free‑Radical Mechanism, What Reactivity Ratios Govern Copolymer Composition?

Free‑radical bulk copolymerization of maleimide (M₁) with methyl acrylate (M₂) at 60°C using 0.1 mol% AIBN initiator yields composition drift that is well described by the terminal model with reactivity ratios r₁ = 0.02 and r₂ = 2.8 (Fineman‑Ross, ¹³C NMR end‑group analysis). The azeotropic composition occurs at a monomer feed ratio of 18 mol% maleimide, producing a copolymer with a glass transition temperature of 92°C (ASTM E1356‑08(2021), midpoint) and a tensile modulus of 2.8 GPa (ASTM D638‑14, Type V specimen, 1 mm·min⁻¹). Because maleimide does not homopolymerise effectively under these conditions (homopropagation rate coefficient k_p <100 L·mol⁻¹s⁻¹), copolymer accumulates predominantly in alternating sequences. In contrast, a BMI such as N,N′‑1,3‑phenylene bismaleimide acts as a cross‑linker from the onset, causing gelation at monomer conversions as low as 12%. Thus, maleimide provides a linear copolymer without gel particles, an advantage when optical‑grade films are required; film haze measured per ASTM D1003‑13 is 1.2% for maleimide/methyl acrylate versus 7.8% for a bismaleimide‑containing copolymer at identical thickness (50 µm).

Long‑term storage stability depends on exclusion of both moisture and amines. When sealed under nitrogen and maintained at a storage temperature ≤ 10°C, the product exhibits a shelf‑life of 24 months with less than a 0.3% increase in maleamic acid content. Once a container is opened, the material should be re‑dried at 40°C under vacuum for 4 h if ambient relative humidity exceeds 60%. Contamination with primary or secondary amines must be avoided: even 50 ppm of triethylamine in solvent causes a 7% drop in active maleimide content within 24 h at 25°C as gauged by UV absorbance at 295 nm.

HS Code	629040
Name	2,5-Dioxo-3-Pyrroline~1H-Pyrrole-2,5-Dione
Molecular Formula	C4H2N2O3
Molar Mass	126.07 g/mol
Appearance	Yellow - orange solid
Melting Point	225 - 227 °C
Solubility	Soluble in polar organic solvents like DMSO, DMF
Density	1.68 g/cm³
Pka	No data found
Flash Point	No data found
Refractive Index	No data found

Packing	100g of 2,5 - Dioxo - 3 - Pyrroline - 1H - Pyrrole - 2,5 - Dione packaged in a sealed bottle.
Shipping	2,5 - Dioxo - 3 - Pyrroline~1H - Pyrrole - 2,5 - Dione is likely shipped in sealed, corrosion - resistant containers. Strict adherence to chemical transport regulations ensures safe transit, protecting from environmental exposure and potential hazards.
Storage	2,5 - Dioxo - 3 - Pyrroline - 1H - Pyrrole - 2,5 - Dione should be stored in a cool, dry place, away from heat sources and direct sunlight. It should be kept in a tightly - sealed container to prevent moisture absorption and exposure to air, which could potentially lead to decomposition or chemical reactions. Store it in a location separate from incompatible substances to ensure safety.

2,5-Dioxo-3-Pyrroline~1H-Pyrrole-2,5-Dione